Wait for pidfile to exist when starting with Redhat init script

Fixes #5359

Docker-DCO-1.1-Signed-off-by: Chris St. Pierre <chris.a.st.pierre@gmail.com> (github: stpierre)
added timeout when waiting for docker pidfile

Docker-DCO-1.1-Signed-off-by: Chris St. Pierre <chris.a.st.pierre@gmail.com> (github: stpierre)
Merge pull request #5844 from stpierre/init-script-wait-for-pidfile

Wait for pidfile to exist when starting with RedHat init script