error handling

[naturallymitchell]

for expected cases
instead of throwing stack trace

[naturallymitchell]

permission denied currently goes:

2019-01-16 14:51:26 ERROR: 	failed to make directory '/usr/share/gut': Permission denied; class=Os (2)
stack traceback:
	[C]: in field 'clone'
	/usr/local/bin/machu-picchu/utils/fetch.lua:18: in function 'fetch'
	/usr/local/bin/machu-picchu/modules/install/install.lua:12: in function 'modules/install/install'
	/usr/local/bin/machu-picchu/modules/mod.lua:6: in function </usr/local/bin/machu-picchu/modules/mod.lua:6>
	/usr/local/bin/machu-picchu/init.lua:58: in local 'init_f'
	[string "?"]:15: in function <[string "?"]:11>
	[C]: in function 'xpcall'
	[string "?"]:11: in main chunk

here's debian's:

E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?

[naturallymitchell]

jazzdotdev/jazz#1