Try to mount Pico drive if not already present (#175)

Fixes #27

As @vslinuxdotnet discovered, sometimes the Pico firmware update emulated USB
stick does not get automounted under Linux.  Add logic to attempt to use
standard tools to mount it to the uploader, only tried if no drives are
detected normally.

tools/uf2conv.py

@@ -33,6 +33,7 @@ import os
 import os.path
 import argparse
 import time
+import glob
 
 toolspath = os.path.dirname(os.path.realpath(__file__)).replace('\\', '/') # CWD in UNIX format
 try:
@@ -357,6 +358,13 @@ def main():
                 args.output = "flash." + ext
         else:
             drives = get_drives()
+            if (len(drives) == 0) and (sys.platform == "linux"):
+                rpidisk = glob.glob("/dev/disk/by-id/usb-RPI_RP2*-part1")
+                try:
+                    subprocess.run(["udisksctl", "mount", "--block-device", os.path.realpath(rpidisk[0])])
+                    drives = get_drives()
+                except:
+                    pass # If it fails, no problem since it was a heroic attempt
 
         if args.output:
             write_file(args.output, outbuf)