Cellular: minor fix to CellularDevice and adding updating unit tests after refactoring

[jarvte]

Description

Updated cellular unit tests after major refactor and introducing new class CellularContext.
Tests couldn't be done properly without the fix to class CellularDevice.cpp which was found while making unit tests.
Fix enables application to retry operation as internal state machine is deleted in case of failure when initializing state machine.

@AriParkkila @mirelachirica please review.

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[0xc0170]

travis-ci/astyle — Passed, 62 files (+4 files)

Note, astyle will error soon on master. Please fix

[jarvte]

@0xc0170 astyle run and fixed. What is the preferred way to run astyle?
For example cellular I use the following:
astyle -n --options=.astylerc --recursive features/cellular/.cpp
astyle -n --options=.astylerc --recursive features/cellular/.h

[0xc0170]

@jarvte Also *.c files :-) But yes, the command looks fine. Sorry to request one more but would like to see it, if you rebase on top of latest master, we would get a new travis config and updated number of files (it was updated this morning, astyle should report 2 files only - we will fix it). Not mandatory though

[jarvte]

@0xc0170 rebase done

[0xc0170]

I am checking travis failure, script is being terminated and reports an error 😕

[0xc0170]

@jarvte Can you add this commit here (https://github.com/ARMmbed/mbed-os/pull/8769/files) - should fix the error

[0xc0170]

Travis astyle fixed 👍

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3647
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8751/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 3254
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8751/

[mbed-ci]

Test : SUCCESS

Build number : 3426
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8751/3426