Fix problems on Ubuntu
Fix problems on Ubuntu

Allow devices with missing a serial port to show up on Ubuntu.  Also
fix regular expression for parsing the ID.  For example the following
string:
"usb-MBED_DAPLINK_VFS_0231023440424e0c000000000000000000000000bd89b3c5-0:0 -> ../../sdb"

Would match with "DA" since those are both valid hex characters
preceded by an underscore.

mazimkhan/mbed-ls,mtmtech/mbed-ls,mtmtech/mbed-ls,jupe/mbed-ls,jjones646/mbed-ls,jupe/mbed-ls,mazimkhan/mbed-ls,jjones646/mbed-ls