core: Add executePipe

Change-Id: I4a434fbe1308ac2f603b8ae09756354c11138912
Related-To: https://bugzilla.redhat.com/1059286
Signed-off-by: Yedidyah Bar David <didi@redhat.com>
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>
core: expose preexec_fn at command execution

Change-Id: I807b8bb6b09e7c16ad767a33f54b1e4a2f1f6eed
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>