In place of two slightly different regexes for 2g/3g and 2g/3g/4g modems
we now use only one regex with conditional patterns for both supported
and current Bands detection.
Adding also minor fix in test code
GE910 is a 2g only modem and when queried for bands it returns
only a 2g set of bands:
--> 'AT#BND=?<CR>'
<-- '<CR><LF>#BND: (0-3)<CR><LF><CR><LF>OK<CR><LF>'
Current regex fails, since it considers the 3g bands block mandatory.
A similar problem happens for current bands.
This patch modifies the regular expressions for properly
supporting GE910 and updates tests.
