syslog-lib.sh bash posix compliance

/opt/ltp/testcases/bin/syslog02: 69: [: syslog-ng: unexpected operator
+ [ syslog-ng == syslog-ng ]
Accoding to:
http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html
[ STRING1 == STRING2 ]  True if the strings are equal. "=" may be
used instead of "==" for strict POSIX compliance.

Because of busybox and other bash like shells look for posix syntax
make it so.

Signed-off-by: Maxim Uvarov <maxim.uvarov@linaro.com>
Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>