don't clean libexec
remove explicit skip_clean of libexec

libexec is now exempt from cleaning
apache-forrest: add 0.9 bottle.
glassfish: add 4.0 bottle.
ringojs: add 0.10 bottle.
scm-manager: add 1.39 bottle.
tomcat: update 8.0.12 bottle.
tomee-jax-rs: add 1.6.0.2 bottle.
tomee-plus: add 1.6.0.2 bottle.
tomee-webprofile: add 1.6.0.2 bottle.
voldemort: add 1.4.0 bottle.