Get Perforce Alternat Roots to Work

From the perforce docs

"If you have any AltRoots: configured, your Perforce client program compares the current working directory against the main Root: first, and then against the alternate roots, and uses the first root that matches the current working directory as the workspace root for that command. If no roots match, the main workspace root is used."

That means that currently perforce will not be able to find any of the roots and will default to the main root. If this main root doesn't exist it creates it within the current working directory (wherever bamboo is running from).

The only solution to this is to determine which root exists before hand and set the running directory to this. This is relatively substantial change to the perforce back-end.

For now we not build unless the main root exists, to avoid the whole alt root problem.