gypv8sh; only catch CalledProcessException, rather than Exception

The try around subprocess.check_call catches Exception. Instead catch CalledProcessException so that other exceptions aren't swallowed.

Due to a confluence of other problems, this was eating an exception that subprocess was raising before actually starting the subprocess.

ref: http://docs.python.org/library/subprocess.html#subprocess.check_call

R=scr@chromium.org

[Sheridan Rawlins, 2012-05-18 21:05:46]

lgtm