[sb2] Add sb2-common and use it to set SBOX_HOME_DIR

sb2-common is installed under /usr/share/scratchbox2/lib/ and
sourced from there to set the sbox home dir.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[sb2] Minor fixes to main makefile and packaging

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[sb2-config] Add -V and -Q options to sb2-config

Use the -V option with -l or -f to highlight the default
sb2 target with a '*'

Use sb2-config -Q to print the sbox home directory

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>