fix MYSQL_UNIX_PORT variable not set because of pipe process env (tes…

[regilero]

…ted on Centos6.7)

http://mywiki.wooledge.org/BashFAQ/024 "I set variables in a loop that's in a pipeline. Why do they disappear after the loop terminates? Or, why can't I pipe data to read?" -> because the pipeline+while is a process in another scope. On the solutions I've tested the mkfifo and it fixed my env.

My env: Centos 6.7 MYSQl_SOCK_PATHS="/srv/data/mysql/mysql.sock"

[kiorky]

See also https://github.com/kiorky/db_smart_backup/commit/758cc0a0e4d27417861cf3b8c155f2a85fc13a58

& 419885abbd8612e6a8b4360558cc319b78369706

[regilero]

@kiorky tested new version, issue fixed, thanks.