Unset SHELL_VERBOSITY environment variable before execution of command

[Naktibalda]

While testing Codeception, I noticed that some cli tests fail when Codeception is executed with -v flag.

For example RunSkippedCept:

Codeception$ ./codecept run cli RunSkippedCept
Codeception PHP Testing Framework v5.0.6 https://helpukrainewin.org

Cli Tests (1) -----------------------------------------------------------------------------------------------------------------------
✔ RunSkippedCept: Run skipped test (0.09s)
-------------------------------------------------------------------------------------------------------------------------------------
Time: 00:00.283, Memory: 8.00 MB

OK (1 test, 3 assertions)

Codeception$ ./codecept run cli RunSkippedCept -v
Codeception PHP Testing Framework v5.0.6 https://helpukrainewin.org

Cli Tests (1) -----------------------------------------------------------------------------------------------------------------------
Modules: Filesystem, Cli, CliHelper, CodeHelper, Asserts
-------------------------------------------------------------------------------------------------------------------------------------
✖ RunSkippedCept: Run skipped test (0.09s)
-------------------------------------------------------------------------------------------------------------------------------------
Time: 00:00.286, Memory: 8.00 MB

There was 1 failure:
1) RunSkippedCept: Run skipped test
 Test  tests/cli/RunSkippedCept.php
 Step  See in shell output "run with `-v` to get more info"
 Fail  Failed asserting that 'Codeception PHP Testing Framework v5.0.6 https://helpukrainewin.org\n
\n
Skipped Tests (1) -------------------------------------------------------------------------------------------------------------------\n
Modules: SkipHelper\n
-------------------------------------------------------------------------------------------------------------------------------------\n
S SkipMeCept: Skip it\n
-------------------------------------------------------------------------------------------------------------------------------------\n
Time: 00:00.019, Memory: 6.00 MB\n
\n
There was 1 skipped test:\n
1) SkipMeCept: Skip it\n
 Test  tests/skipped/SkipMeCept.php\n
OK, but incomplete, skipped, or useless tests!\n
Tests: 1, Assertions: 0, Skipped: 1.' contains "run with `-v` to get more info".

Scenario Steps:

 5. $I->seeInShellOutput("run with `-v` to get more info") at tests/cli/RunSkippedCept.php:9
 4. $I->seeInShellOutput("OK, but incomplete, skipped, or useless tests!") at tests/cli/RunSkippedCept.php:8
 3. $I->seeInShellOutput("S SkipMeCept: Skip it") at tests/cli/RunSkippedCept.php:7
 2. $I->executeCommand("run skipped SkipMeCept.php") at tests/cli/RunSkippedCept.php:6
 1. $I->amInPath("tests/data/sandbox") at tests/cli/RunSkippedCept.php:5

During investigation I discovered that \Symfony\Component\Console\Application::configureIO method sets SHELL_VERBOSITY variable which affects verbosity of the child process:
https://github.com/symfony/console/blob/3e294254f2191762c1d137aed4b94e966965e985/Application.php#L958

\Symfony\Component\Console\Tester\ApplicationTester unsets SHELL_VERBOSITY too, so it seems like a good approach to unset it in Cli::runShellCommand.