Simplify signing procedure, now it get values automatically from keystore.properties if present

[ale5000-git]

@mar-v-in

Simplify signing procedure, now it get values automatically from keystore.properties if present;
in addition it can optionally get the Keystore password from KEYSTORE_PASSWORD env variable.

INSTRUCTIONS
Just place the keystore file keystore.jks and a file called keystore.properties in the main folder of the repo (on your local PC only).
If the file keystore.properties is missing it will compile an unsigned build.

Example of keystore.properties:

storeFile=keystore.jks
keyAlias=my_alias
keyStorePassword=my_password

Instead to use the password from env the keystore.properties should be:

storeFile=keystore.jks
keyAlias=my_alias
fallbackToEnv=true

and you must set the the env var KEYSTORE_PASSWORD.

[mar-v-in]

That's actually what the loading of user.gradle is for: to allow for a custom signing configuration. Configurations might be more complex or need special features (e.g. when signing with a lineage), so I thought that providing an easy anchor to add custom configurations to build.gradle would be the easiest way to realize this.

[ale5000-git]

Yes, user.gradle could be useful for more complicate things but for the casual user that do simple changes and want to test them, this one is really simpler.

It also allow to set a single configuration even when there are many subprojects.

Edit: In addition my keystore.properties and user.gradle are cumulable, so they can also use both together.
Edit 2: In case it get merged I will also update the wiki.

[mar-v-in]

I close this pull request as the FakeStore source code is now maintained in the vending-app folder in GmsCore repository.