Review 26396

C. Thomas Tyler
Added delay on start, to workaround common issues where
a fast cycle of p4d process fails because the TCP port
(e.g. 1666) is still in use briefly after a clean shutdown,
a system resource isn't available immediately on boot, or
similar timing issue.

The delay on start is skipped if P4ROOT is empty (tested for
by checking for existence of db.comain).

Added optional new SDP_START_DELAY setting in the p4_vars file
(generated from p4_vars.template) to configure the delay.

Files in this changelist now pass shellcheck (v0.61) (driving
various minor non-functional edits).
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