Custom policy for nova-api tmpfs errors

This policy fixes an issue whereby nova-api is unable to use tmpfs,
/dev/shm, when SELinux is running in enforcing mode.

Partial-Bug: 1342863
Change-Id: I51d2afbd89c4f632920eca6d2d1698665ccf4e21
Merge "Custom policy for nova-api tmpfs errors"