Keychain path is used in xcodebuild, .keychain extension was added to a keychain name, /tmp is used as a temp directory

Seems like signing was failing on some machines. Probably because of wrong keychain specification.
Seems like extension adding is not too much. The full keychain file path is used in xcodebuild.
Temporary directory path was looking weird so, as we might assume that the build would be run on OS X, /tmp is used as a temp directory.
Additional xcodebuild parameters tokenizing was added

Previously, if there were added more then one additional xcodebuild parameter – all of them were joined and added as one string parameter.
Tokenizing allows to break additional paramters string to pieces and to add them in a cycle.
Parameters (tokens) retrieving method was taken from cmdAsSingleString(String s) function of Jenkins' ProcStarter class.
EnvVars expanding was added for configuration parameters

As envVars are not expanded by launcher, it's needed to expand (i.e. apply) them manually.
Expanded was added for xcworkspacePath, xcodeprojPath, target, scheme, configuration, additionalParameters and artifactsTemplate.