Cellular: AT debugging improved

[AriParkkila]

Description

• Removed function entry debug prints
• AT debug is less noisy and it now prints also written chars
• AT debug can be enabled using "cellular.debug-at" flag
• Cellular log now has atomic locks for tracing
• Changed non-fatal error prints to less severe
• Fixed cellular Greentea tests
• ATHandler::read was fixed to handle zero length string ""
• Renamed enable_debug to set_debug, that's API change but only for debugging
• Removed obsolete FEATURE_COMMON_PAL flag from trace (CI fixed on Lora: Remove obsolete FEATURE_COMMON_PAL flags #6905)

Pull request type

[ ] Fix
[X] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[AriParkkila]

@mirelachirica @jarvte please review

[0xc0170]

@AriParkkila Please review astyle travis info about changes (it shows diff of style issues in touched files).

[AriParkkila]

Please proceed with this.

[0xc0170]

/morph build

[cmonr]

Odd. Not sure why a failure wasn't reported.

/morph build

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2126
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6927/

Triggering tests

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

[cmonr]

Shuffling around some jobs.

/morph export-build

[cmonr]

/morph test

[cmonr]

Performing another shuffle. Attempting to make sure #6993 is ready by the AM, if needed.

/morph export-build

[mbed-ci]

Test : FAILURE

Build number : 1924
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6927/1924

[cmonr]

@AriParkkila Looks like this will need #6993 to pass. The test error is a newly discovered one that was found today.

That PR should be tested, merged, and ready to be rebased by the AM.

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1760
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6927/

[kjbracey]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2137
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6927/

Triggering tests

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

[mbed-ci]

Test : SUCCESS

Build number : 1932
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6927/1932

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1764
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6927/