Add configCacheFileMode option

[mougrim]

Q	A
Documentation	no
Bugfix	no
BC Break	no
New Feature	yes
RFC	no
QA	no

Description

Tell us about why this change is necessary: Config file can contain some secret information, which should not be readible for all users in server. So I need to provide config file permission configCacheFileMode option, e.g. 0600.

• Are you adding documentation?

  • No

• Are you providing a QA improvement (additional tests, CS fixes, etc.) that does not change behavior?

  • I've added test for new option

• Are you fixing a BC Break?

  • Threre is no BC Break

• Are you adding something the library currently does not support?

  • Вescribed above

• Are you refactoring code?

  • No

[Xerkus]

This change needs tests to ensure file mode is picked up and applied properly.