Increased timeout for Heat OSTF test

We had small timeout for Heat stack creation operation
and this commit will fix it to 10 minutes. Heat stack
with small image should be created for this time on any
environments, even with small amount of RAM.

Change-Id: I2660a5c607ff6f11219c6e24dee10d13f50cf5e3
Closes-Bug: #1331472
(cherry picked from commit f91ee37cfc3705cdf78d1b637b6bd8423b874409)