core: Hide pushd popd output in db scripts

pushd and popd outputs by default the content of the directory stack to
std. When we are using dbscripts scripts, we are changing directories
implicitly and would like to hide this output from the user.

Change-Id: I65b5b8a9bde300d5bb74c36e012d27b936363b56
Signed-off-by: Eli Mesika <emesika@redhat.com>