Improve invalid configuration error messages

[theotherjimmy]

old

[ERROR] OrderedDict([(u'help', u'Address of the active application firmware in flash'), (u'value', u'POST_APPLICATION_ADDR'), (u'required', 1)]) is not valid under any of the given schemas,OrderedDict([(u'help', u'Flash sector address for SOTP sector 1'), (u'macro_name', u'PAL_INTERNAL_FLASH_SECTION_1_ADDRESS'), (u'value', [])]) is not valid under any of the given schemas

[ERROR] 1 is not of type u'string'

new

[ERROR] in ./mbed_app.json element config.application-start-address.required: 1 is not of type u'boolean'; in ./mbed_app.json element config.sotp-section-1-address.value: [] is not of type u'integer', u'string', u'boolean', u'null'                                                  

[ERROR] in ./tools/mbed_lib.json element name: 1 is not of type u'string'

bug fix/ui improvement?

@marcuschangarm

[theotherjimmy]

@cmonr Verified working with app and lib config. Could you review?

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 1308
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6240/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 968
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6240/

[mbed-ci]

Test : SUCCESS

Build number : 1092
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6240/1092