Added module to execute commands on certain Sercomm devices through
backdoor
See more: https://github.com/elvanderb/TCP-32764
Moved to more appropriate folder
Code Review Feedback

Removed Payload size restriction. I tested with 10,000 characters and it
worked.
Removed handler for now, since it's unable to get a shell. It's
currently limited to issuing commands.
Removed RequiredCmd options that didn't work successfully.
Removed stupid debug line I left in
Code Review Feedback

Migrated the Sercomm module to use the CmdStager mixin to provide
uploading of the ELF binary.
Modified the CmdStagerEcho mixin to allow bypass of the "-en " since in
this case, the device messed up when it was used, and would actually
write the "-en " to the file, from some flaky busybox version of "echo".
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Fixed some handling of errors and invalid hosts
Add minor fixes, mainly formatting
Delete commas
Merge branch 'review_2823' of https://github.com/jvazquez-r7/metasploit-framework into sercomm_exec
Added tested device
Land #2823, @mandreko's exploit module for OSVDB 101653