BuildSystem: Use single bootstrap.sh for Asterisk and menuselect.

This causes the root bootstrap.sh script to generate configure scripts
for both Asterisk and menuselect.  This ensures that both configure
scripts are generated with the same version of autotools and avoids
situations where shared autoconf macros get modified without
regenerating the menuselect script.

Change-Id: I2bfd8537bbb63b3d46b11efabbb15eaaf9ef731a