Renaming the default loaded "init" scripts and added command line arg for "bare-mode"

- bro.init was renamed to base/init-bare.bro and base/all.bro
  was renamed to init-default.bro.

- To run in "bare mode" with only the init-bare.bro and no other
  scripts from base/, use either -b or --bare-mode.

- The environment variable to run in "bare mode" has been removed.

testing/btest/policy/frameworks/logging/ascii-binary.bro

@@ -1,5 +1,5 @@
 #
-# @TEST-EXEC: BRO_NO_BASE_SCRIPTS=1 bro %INPUT
+# @TEST-EXEC: bro -b %INPUT
 # @TEST-EXEC: btest-diff ssh.log
 
 module SSH;