Support setting access-all-areas security policy for agent code -- fixes BYTEMAN-233

Added new -javaagent option secure:true which causes the agent to add
an access-all-areas security policy -- default is currently false.

Modified bminstall script (bash and Windows) to forward -s option to
BMInstall class requesting setting of security policy

Modified BMUnit code to check for

  -Dorg.jboss.byteman.contrib.bmunit.policy=true

and forward the policy setting to the agent by adding secure:true to
the agent options

Modified Install class to check for -s argument and forward the policy
setting to the agent by adding secure:true to the agent options.