Fix e2e tests on Windows

There were two problems.
 1. Couldn't delete the tmp project dir on Windows because it was the CWD
    dir of the node process and Windows can't delete "busy" dirs.
 2. There was an interaction between tests in spec and those in e2e.
    Jasmine ran the e2e tests first, the CWD stayed in temp dir, but some
    tests in spec assume that CWD is the cordova source root dir.

Both problems solved by process.chdir(<source root>) after each e2e test.