Before, vcsExec() returned already started VcsCommand.
Later, callers of vcsExec() were establishing connections
to the retured VcsCommand::done() signal. However, when
process fails to start (e.g. because of non-existing
executable), the done() signal may be emitted synchonously
from inside VcsCommand::start(). In this scenario
callers of VcsCommand could miss the emission of done()
signal and connect to already finished command.
Instead, provide a vcsExecWithHandler() function which
takes a handler to be called when command finished.
In addition it takes the context object, too.
Don't return VcsCommand from vcsExec() anymore.
Change-Id: I2fb5fbe5d27632ea039c650d37e5d7d1b60cebc0
Reviewed-by: Orgad Shaneh <orgads@gmail.com>