Revert "adjust instance type from m3.medium -> m4.large for f20"
Revert "adjust instance type from m3.medium -> m4.large for f20"

This reverts commit 496fd64f314691e9c8d69ab559105034ce64ab5e.

We also need to update image we use, see
https://github.com/StackStorm/st2cd/commit/496fd64f314691e9c8d69ab559105034ce64ab5e#commitcomment-12901881
for details.

StackStorm/st2cd,StackStorm/st2cd