Improve specificity of `test:unit:lax` npm script (#10661)

The unit test npm script `test:unit:lax` is now more specific about
which tests files to exclude. An `--ignore` CLI option is used to
specify the files to ignore, rather than using the braces glob syntax
to ignore them from the target glob itself.

This makes the option easier to update going forward as we move more
tests into the "strict" group, because the options are exactly the same
between the two scripts. It also ensures we don't accidentally exclude
other subdirectories that happen to also be named `permissions`.

In trying to implement this, I stumbled at first because mocha expects
the ignore pattern to be a relative path if the target is a relative
path (i.e. they need to both start with `./` or neither). The script
`test:unit:strict` has been updated to use a relative target pattern
for consistency.

package.json

@@ -22,8 +22,8 @@
     "sendwithprivatedapp": "node development/static-server.js test/e2e/send-eth-with-private-key-test --port 8080",
     "test:unit": "mocha --exit --require test/env.js --require test/setup.js --recursive './{ui,app,shared}/**/*.test.js'",
     "test:unit:global": "mocha --exit --require test/env.js --require test/setup.js --recursive test/unit-global/*.test.js",
-    "test:unit:lax": "mocha --exit --require test/env.js --require test/setup.js --recursive './{ui,app,shared}/{,**/!(permissions)}/*.test.js'",
-    "test:unit:strict": "mocha --exit --require test/env.js --require test/setup.js --recursive 'app/scripts/controllers/permissions/*.test.js'",
+    "test:unit:lax": "mocha --exit --require test/env.js --require test/setup.js --ignore './app/scripts/controllers/permissions/*.test.js' --recursive './{ui,app,shared}/**/*.test.js'",
+    "test:unit:strict": "mocha --exit --require test/env.js --require test/setup.js --recursive './app/scripts/controllers/permissions/*.test.js'",
     "test:unit:path": "mocha --exit --require test/env.js --require test/setup.js --recursive",
     "test:e2e:chrome": "SELENIUM_BROWSER=chrome test/e2e/run-all.sh",
     "test:e2e:chrome:metrics": "SELENIUM_BROWSER=chrome mocha test/e2e/metrics.spec.js",