Update sanity tested distros

Change-Id: I11475457ef1178f15ddf4e26300b9b1f37c064cc
Reviewed-by: Mikko Gronoff <mikko.gronoff@qt.io>

conf/distro/b2qt.conf

@@ -46,6 +46,7 @@ SANITY_TESTED_DISTROS += " \
             LinuxMint-14 \n \
             LinuxMint-16 \n \
             LinuxMint-17.1 \n \
+            LinuxMint-18.1 \n \
             "
 
 SYSVINIT_ENABLED_GETTYS = ""