pgsql: In pg_upgrade, try a few times to open a log file.

In pg_upgrade, try a few times to open a log file.

If we call pg_ctl stop, the server might continue and thus
hold a log file for a short time after it has deleted its pid file,
(which is when pg_ctl will exit), and so a subsequent attempt to
open the log file might fail.

We therefore try to open it a few times, sleeping one second between
tries, to give the server time to exit.

This corrects an error that was observed on the buildfarm.

Backpatched to 9.2,

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/bdf8f58397dc83618dccd8f85a46a02933a7f86f

Modified Files
--------------
contrib/pg_upgrade/exec.c | 23 ++++++++++++++++++++++-
1 files changed, 22 insertions(+), 1 deletions(-)