Update JAVA_HOME detection for Fedora 20 and newer

This updates the logic for detecting JAVA_HOME to include new explicit
paths for JAVA_HOME based on the install path for openjdk 1.7.0 on
Fedora 20.
Fall back to non-powerline font on TERM=linux

The default linux console does not by default support powerline style
fonts. This patch insures that the presence of the Linux term variable
degrades the prompt to the previous setting.