Enusre to download sources in cliClient
cliClient is the better place to call cliClient.sources to download sources
files. This makes it easier for downstream client tool to extend
cliClient.sources and no need to overwrite related methods to use the
extension, where the related methods are compile, install, prep, local and
srpm.
Signed-off-by: Chenxiong Qi <cqi@redhat.com>