EX-4141 lipe: lamigo should detect dead OST and restart ALR

EX-4141 lipe: lamigo should detect dead OST and restart ALR

Use '# keepalive' message and ssh read with timeout
to detect OST is down and restart ALR.
Add stats for ALR last seen message

To make lamigo compatible with older
ofd_access_log_reader lamigo can work in two modes:
1. lamigo does not expect '# keepalive' message.
In this case after timeout it will restart
ofd_access_log_reader silently
2. lamigo expects periodical # keepalive
message. If lamigo does not receive keepalive message
or any other message from ofd_access_log_reader
within timeout it reports error message and
restarts ofd_access_log_reader.
lamigo switches from 1 to 2 once it receives
'# keepalive' message

Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Test-Parameters: trivial testlist=hot-pools
Change-Id: I55bc92b03ef5b45b72ff59ffd4b450cd1927cdb0
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48647
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>