[ios][detox] Use PIPESTATUS instead of grepping a file to get xcodebuild's exit code
[ios][detox] Use PIPESTATUS instead of grepping a file to get xcodebuild's exit code

This uses the actual exit code instead of grepping for strings in the output. Tested

exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent