base.bbclass: increase indent in get_layers_branch_rev() and buildcfg_vars()

base.bbclass: increase indent in get_layers_branch_rev() and buildcfg_vars()

Although it may not appeal so much to users to prefer 80x24 consoles,
the general trend is for screens to get bigger and the current output
has started to look a little cramped on a modern HD display.

Increasing from 17 to 20 is obviously arbitrary, but does give enough
space to cleanly display layers such as "meta-nodejs-contrib" and
"meta-virtualization" while still keeping the output fairly compact.

(From OE-Core rev: e556b85a452a4ebf34a0c9581608f135bbad2e2c)

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>