iOS: Support for filtering Test Configurations

[zuziakaxel]

Currently Flank supports .xctestrun file from Test Plan #685, but user is not able to specify which test configuration Flank should run.
For example if .xctestrun file contains 2 configurations Flank will run both of them.

FTL doesn't support specifying test configuration yet, so Flank needs to handle this on his side.

Example: We have .xctestrun file containing two test configurations: pl and en:

{
  "en": [ // test configuration: en
    [
      "UITestsClass/test1_ENLocale"
    ]
  ],
  "pl": [ // test configuration: pl
    [
      "UITestsClass/test1_ENLocale"
    ]
  ]
}

Actual result:

Flank will generate two .xctestrun files for each configuration and run two separate test runs on FTL.

Expected result:

User should be able to specify which configuration Flank should run by passing argument: (proposal - to be discussed)

 -only-test-configuration: en

or

-skip-test-configuration: pl

---

Proposed argument names are from actual xcodebuild test-without-building command. Reference:
man xcodebuild

 -skip-test-configuration  test-configuration-name,

    -only-test-configuration test-configuration-name
       Constrain      test     configurations     in     test     actions.
       -only-test-configuration constrains a test action to  only  test  a
       specified  test  configuration  within a test plan, and exclude all
       other test configurations.  -skip-test-configuration  constrains  a
       test action to skip a specified test configuration, but include all
       other test configurations. Each test configuration name must  match
       the  name  of a configuration specified in a test plan and is case-
       sensitive. An xcodebuild command can  combine  multiple  constraint
       options,   but   -only-test-configuration   has   precedence   over
       -skip-test-configuration.