Add support for projectFile in subdirectory

[phatblat]

Currently, the build fails with a message like the following if the *.xcodeproj file is not in the same directory as the build.gradle file:

xcodebuild: error: The directory /Users/me/path/to/repo/GradleXcodeIssueDemo does not contain an Xcode project or workspace.

This PR adds support for this by adding a -project parameter to the xcodebuild command using the projectFile property.

This change can be validated in the ben/fixes branch of my fork of the example project

resolves #287

[coveralls]

Coverage increased (+0.05%) to 70.984% when pulling f3d887e on phatblat:ben/project-in-subdir into a86b9e7 on openbakery:develop.

[renep]

This does not work :-(

At my Test-Projects I'll get:

14:57:26.673 :xcodebuild FAILED
14:57:26.680 
14:57:26.680 FAILURE: Build failed with an exception.
14:57:26.681 
14:57:26.681 * What went wrong:
14:57:26.681 Execution failed for task ':xcodebuild'.
14:57:26.681 > Command failed to run (exit code 64): '/Applications/Xcode.app/Contents/Developer/usr/bin/xcodebuild -scheme SwiftExample -project /Users/groundskeeper/Go/pipelines/GXP-Example-ios-Swift-Continuous/example/iOS/SwiftExample/SwiftExample.xcodeproj -workspace SwiftExample.xcworkspace -configuration Debug CODE_SIGN_IDENTITY= CODE_SIGNING_REQUIRED=NO -derivedDataPath /Users/groundskeeper/Go/pipelines/GXP-Example-ios-Swift-Continuous/example/iOS/SwiftExample/build/derivedData DSTROOT=/Users/groundskeeper/Go/pipelines/GXP-Example-ios-Swift-Continuous/example/iOS/SwiftExample/build/dst OBJROOT=/Users/groundskeeper/Go/pipelines/GXP-Example-ios-Swift-Continuous/example/iOS/SwiftExample/build/obj SYMROOT=/Users/groundskeeper/Go/pipelines/GXP-Example-ios-Swift-Continuous/example/iOS/SwiftExample/build/sym SHARED_PRECOMPS_DIR=/Users/groundskeeper/Go/pipelines/GXP-Example-ios-Swift-Continuous/example/iOS/SwiftExample/build/shared -destination platform=iOS Simulator,id=4E839F12-B70E-4973-AC91-231836EF9045'
14:57:26.681   Tail of output:
14:57:26.681   xcodebuild: error: You cannot specify both an Xcode project and a workspace.

[phatblat]

Ah, there needs to be some logic around when to use projectFile vs workspace.