Generate jdk_switcher without sudo

The idea is to save $PATH when jdk_switcher is first sourced,
and prepend the desired $JAVA_HOME/bin to the saved value whenever
we switch the JDK version
Do not hard code default version for 'print'
Remove unnecessary assignment
Merge pull request #333 from travis-ci/ha-feature-jdk_switcher-without-sudo

Eradicate use of sudo from jdk_switcher_rc