Enforce the release is performed only from RHEL 6.5 or equivalent

Motivation:

Netty must be released from RHEL 6.5 x86_64 or compatible so that:

1) we ship x86_64 version of epoll transport officially, and
2) we ensure the ABI compatibility with older GLIBC versions.
   The shared library built on a distribution with newer GLIBC will not
   run on older distributions.

Modifications:

- When 'release' profile is active, perform an additional check using
  maven-enforcer-plugin so that 'mvn release:*' fails when running on
  non-RHEL6.5.  This rule is active only when releasing, so a user
  should not be affected.
- Simplify maven-release-plugin configuration by removing redundant
  profiles such as 'linux'.  'linux' is automatically activated when
  releasing because we now enforce the release occurs on linux-x86_64.
- Remove the no-osgi profile, which is unused
- Remove the reference to 'sonatype-oss-release' profile in all/pom.xml,
  because we always specify 'release' profile when releasing
- Rename the profile 'linux-native' to 'linux' for brevity
- Upgrade oss-parent and maven-enforcer-plugin

Result:

No one can make a mistake to release Netty on an environment that can
produce incompatible or missing native library.