Scripts for finding accidental secrets in the repo.

This adds the following:
- A detect-secrets dependency and a related script
  (`script/detect_secrets`) to find and alert developers to secrets
  added to the code. By default, the script will search staged and new,
  unstaged files. It can optionally search only staged files.
- A whitelist, `.secrets.baseline`, that tracks instances of secrets or
  false positives already in the repo.
- Modifies `script/test` to detect secrets as part of the test suite.
- Updates to the README regarding the use of detect-secrets.

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "d697cd7c279a761283ea2ffefab08d5854e4c0341b5646839b269ab0d999bf87"
+            "sha256": "f09d90a1b4b86eff2e0ed453ceefcce4f19d54c57fb50ebed1f02aae8ab83c2a"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -71,18 +71,18 @@
         },
         "boto3": {
             "hashes": [
-                "sha256:666f37c5852f71925494fc2103b189deafe6702c1d9ae60bead5b1b6466de857",
-                "sha256:7b77b507221ec15550b02d492804166bcc61ef3a81312968065515a76aa1791b"
+                "sha256:3ec5b520dbd0a430cdd581a8250991fb0f21ee7e668a8928f15006b312fa86dc",
+                "sha256:8aec0247131a0db1e33d28ad13910e01e6dfa208e8ab8ee5a4095e92dbaabf45"
             ],
             "index": "pypi",
-            "version": "==1.9.202"
+            "version": "==1.9.204"
         },
         "botocore": {
             "hashes": [
-                "sha256:71ca578701e746fe947c098e5dee06128d0f6ba98217ba7e29aff0dab8caf82f",
-                "sha256:e55003c46e71396a551d4b70f39286f8fc4094ac6cf90f5db8d7a68bb4af1f9d"
+                "sha256:56cd1114e0ce35733e890b321160c8c438243f4fa54d3d074dfa6bdce4ee55aa",
+                "sha256:f86504bcc9c44d5b2e7b019f2f279b70f17b1400d2fc4775bc009ec473530cad"
             ],
-            "version": "==1.12.202"
+            "version": "==1.12.204"
         },
         "certifi": {
             "hashes": [
@@ -562,6 +562,20 @@
             "index": "pypi",
             "version": "==1.4"
         },
+        "certifi": {
+            "hashes": [
+                "sha256:046832c04d4e752f37383b628bc601a7ea7211496b4638f6514d0e5b9acc4939",
+                "sha256:945e3ba63a0b9f577b1395204e13c3a231f9bc0223888be653286534e5873695"
+            ],
+            "version": "==2019.6.16"
+        },
+        "chardet": {
+            "hashes": [
+                "sha256:84ab92ed1c4d4f16916e05906b6b75a6c0fb5db821cc65e70cbd64a3e2a5eaae",
+                "sha256:fc323ffcaeaed0e0a02bf4d117757b98aed530d9ed4531e3e15460124c106691"
+            ],
+            "version": "==3.0.4"
+        },
         "click": {
             "hashes": [
                 "sha256:2335065e6395b9e67ca716de5f7526736bfa6ceead690adf616d925bdc622b13",
@@ -615,6 +629,14 @@
             ],
             "version": "==4.4.0"
         },
+        "detect-secrets": {
+            "hashes": [
+                "sha256:33593cbf7099ced595e7371fcee31c815a237419de2869d571bbdb651a125d4c",
+                "sha256:7b8e6d521f5a164ff17dbe3d2691eb85f842133d4e6bb7a23eeb461a0ab4e215"
+            ],
+            "index": "pypi",
+            "version": "==0.12.5"
+        },
         "docopt": {
             "hashes": [
                 "sha256:49b3a825280bd66b3aa83585ef59c4a8c82f2c8a522dbe754a8bc8d08c85c491"
@@ -666,6 +688,13 @@
             "index": "pypi",
             "version": "==1.0.1"
         },
+        "idna": {
+            "hashes": [
+                "sha256:c357b3f628cf53ae2c4c05627ecc484553142ca23264e593d327bcde5e9c3407",
+                "sha256:ea8b7f6188e6fa117537c3df7da9fc686d485087abf6ac197f9c46432f7e4a3c"
+            ],
+            "version": "==2.8"
+        },
         "importlib-metadata": {
             "hashes": [
                 "sha256:23d3d873e008a513952355379d93cbcab874c58f4f034ff657c7a87422fa64e8",
@@ -945,6 +974,14 @@
             "index": "pypi",
             "version": "==5.1.2"
         },
+        "requests": {
+            "hashes": [
+                "sha256:11e007a8a2aa0323f5a921e9e6a2d7e4e67d9877e85773fba9ba6419025cbeb4",
+                "sha256:9cf5292fcd0f598c671cfc1e0d7d1a7f13bb8085e9a590f48c010551dc6c4b31"
+            ],
+            "index": "pypi",
+            "version": "==2.22.0"
+        },
         "selenium": {
             "hashes": [
                 "sha256:7491b5391f29a74774d475456d3a138e00fae0b3966f68a100f1f3ad331ce166",