add --dont-scan (-D) command line option

add --dont-scan (-D) command line option

Introduce the -D or --dont-scan command line option. This avoids
automatic driver scans, and exclusively uses what -d specifies.

Some device drivers use non-standard protocol features since their
supported devices don't support the corresponding standard mechanisms.
Which can confuse conforming devices. In these situations it can be
desirable to not scan automatically for available devices, instead do
nothing until callers will specify the -d option.

This change is motivated by but does not resolve bugs #1155 and #1373.