install_prereq: Check if is installed aptitude otherwise to install.

install_prereq: Check if is installed aptitude otherwise to install.

If in Debian or system based, dont have aptitude installed the script do
nothing. This patch checked if aptitude  installed, if not installed.

Also, if execute script with all packages installed yet, the script not show
nothing and return exit 1 because the command 'grep' get nothing from pipe from
'awk'.

ASTERISK-25113 #close
Reported By: Rodrigo Ramírez Norambuena <decipher.hk@gmail.com>

Change-Id: Iebdff55805d3917166e5e08e0a1e2176f36ff27f