mbed CLI 0.9.10 fixes

[screamerbg]

Fixed:

• Git re-association with tip of a branch matching the checkout hash, where local and remote branches were treated as same entity (and they might be different if the user hasn't merged with the latest origin/branch). As reported mbed updatedoes not update libraries if branch is checked out. mbed-os#3037
• Handling of arbitrary .lib files
• Pylint fixes (9.9/10)

Reviewers:

• Review by @SeppoTakalo
• Review by @sg-

[SeppoTakalo]

Seems to fix the ARMmbed/mbed-os#3037

Using 0.9.9:

~/src/mbed-os-example-mesh-minimal/mbed-os$ git describe --long
mbed-os-5.2.0-rc2-0-ga551faa
~/src/mbed-os-example-mesh-minimal/mbed-os$ cd ..
~/src/mbed-os-example-mesh-minimal$ mbed update
[mbed] Updating program "mbed-os-example-mesh-minimal" to latest revision in the current branch
merge: origin/rc3 - not something we can merge
[mbed] Updating library "atmel-rf-driver" to rev #c1b7ba3c2e9a
[mbed] Updating library "mbed-os" to rev #873686ce791c
[mbed] Updating library "mcr20a-rf-driver" to rev #d8810e105d7d
~/src/mbed-os-example-mesh-minimal$ cd mbed-os
~/src/mbed-os-example-mesh-minimal/mbed-os$ git describe --long
mbed-os-5.2.0-rc2-0-ga551faa
~/src/mbed-os-example-mesh-minimal/mbed-os$ mbed --version
0.9.9

With this PR:

~/src/mbed-os-example-mesh-minimal$ mbed update
[mbed] Updating program "mbed-os-example-mesh-minimal" to latest revision in the current branch
merge: origin/rc3 - not something we can merge
[mbed] Updating library "atmel-rf-driver" to rev #c1b7ba3c2e9a
[mbed] Updating library "mbed-os" to rev #873686ce791c
[mbed] Updating library "mcr20a-rf-driver" to rev #d8810e105d7d
~/src/mbed-os-example-mesh-minimal$ cd mbed-os
~/src/mbed-os-example-mesh-minimal/mbed-os$ git describe --long
mbed-os-5.2.0-rc3-0-g873686c
~/src/mbed-os-example-mesh-minimal/mbed-os$ mbed --version
0.9.10