Do not show y/N proposal for Packages that can not be installed

[https://www.google.com/accounts/o8/id?id=AItOawkPb0RtPyicSdU7pLcv1UrX-yCh-YjkOwU]

In interactive mode of Bcfg2 client:

Loaded tool drivers:
 APT      Action   DebInit  POSIX    VCS     
The following entries are not handled by any tool:
 Package:None:apache2       Package:None:mysql-server  Package:None:php5         

The following packages are specified in bcfg2:
 apache2       mysql-server  php5         
The following packages are prereqs added by Packages:


Phase: initial
Correct entries:	0
Incorrect entries:	3
Total managed entries:	3
Unmanaged entries:	264

Install Package: apache2? (y/N): y
Install Package: mysql-server? (y/N): y
Install Package: php5? (y/N): y

Phase: final
Correct entries:	0
Incorrect entries:	3
 Package:apache2       Package:mysql-server  Package:php5         
Total managed entries:	3
Unmanaged entries:	264

It would more intuitive to see the following messages:

...
Unmanaged entries:      264

Can't install Package: apache2 (no plugins can handle operation) [Press Enter]
Can't install Package: mysql-server (no plugins can handle operation) [Press Enter]
Can't install Package: php5 (no plugins can handle operation) [Press Enter]

Phase: final
...

If -d (debug) option is specified, the prompts can also show names of the plugins that will be called to process the command, e.g:

Install Package (Packages,): apache2? (y/N): y
Install Package (Packages,): mysql-server? (y/N): y

[https://www.google.com/accounts/o8/id?id=AItOawnSjgovXZr-_V3vGkvMSR0pc5LDykRc1Nc]

Fixed in ​https://github.com/Bcfg2/bcfg2/commit/fc518559460429af45d889132fbab1d06d92b9ff