[show] Run fwutil with sudo (sonic-net#1364)

**- What I did**
Added ability to run `show platform firmware` commands without `sudo`, as described in the [design document](https://github.com/Azure/sonic-utilities/blob/master/doc/Command-Reference.md#platform-component-firmware-show-commands):

**- How I did it**
Made `show platform firmware` implementation run `fwutil` with `sudo` 

Signed-off-by: Volodymyr Boyko <volodymyrx.boiko@intel.com>

show/platform.py

@@ -133,7 +133,7 @@ def temperature():
 @click.argument('args', nargs=-1, type=click.UNPROCESSED)
 def firmware(args):
     """Show firmware information"""
-    cmd = "fwutil show {}".format(" ".join(args))
+    cmd = "sudo fwutil show {}".format(" ".join(args))
 
     try:
         subprocess.check_call(cmd, shell=True)