SlicingBD: replace second constructor with default parameter

[kegilbert]

Slightly simplifies the SlicingBlockDevice constructor setup. Example in the header still works correctly.

@geky

[0xc0170]

@tommikas Can you look at the CI failure please, does look to me like internal error.

[tommikas]

Yep, Jenkins sometimes throws errors like that. Usually it's not systematic, and this too passed after restarting.

[0xc0170]

@kegilbert First line of the commit msg should not exceed 50 characters (I edited the headline here, please review). You can provide more information in the next paragraph in the commit msg.

[kegilbert]

@0xc0170 I updated the commit and title, thanks for the heads up!

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 346
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/5385/

Triggering tests

/morph test
/morph uvisor-test

[mbed-ci]

Test : FAILURE

Build number : 157
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/5385/157

[geky]

Looks good to me, yay a use for -0

[kegilbert]

[kegilbert]

Looks like all tests for the NCS36510 and NRF51_DK timed out.
@studavekar Should I rekick off the morph test?

[studavekar]

/morph test

[mbed-ci]

Test : SUCCESS

Build number : 165
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/5385/165