More RabbitMQ POSIX error codes

We must add the following POSIX error codes in order to detect node
failure:

• 68 - EX_NOHOST
• 69 - EX_UNAVAILABLE
• 70 - EX_SOFTWARE
• 75 - EX_TEMPFAIL
• 78 - EX_CONFIG

The following commits introduced these return values:

• rabbitmq/rabbitmq-server@7984540175d0b8852025165b6b6a0ac05d692c98
• rabbitmq/rabbitmq-common@92ae50e5964d4f079c7b2abed1caaa8ab54a439b

For the error codes meanings go to:

• http://www.sbras.ru/cgi-bin/www/unix_help/unix-man?sysexits+3
• http://linux.die.net/include/sysexits.h
• https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=misc/sysexits.h;hb=HEAD

Note that the following error valies do not mean that the node is
stopped and therefore doesn't covered by this commit:

• 64 - EX_USAGE
• 65 - EX_DATAERR
• 67 - EX_NOUSER

Signed-off-by: Peter Lemenkov <lemenkov@redhat.com>