linuxboot: restructure linuxboot build script

Changes to restructure the build-test-linuxboot.sh script:

1. Use Go version 1.17.11 and use the tag v0.9.0 to clone u-root repo.

2. Add seperate functions to install Golang, u-root and add checks in
the setup functions to remove directories in case of incomplete
installations/setup-failures. This enables the script to setup/build the
components separately.

3. Add explicit command in linuxboot-uroot-automation.sh script to
create mount point before mounting the stage-2 linuxboot disk image to
avoid mounting-related failures.

Signed-off-by: Shriram K <shriram.k@arm.com>
Change-Id: I54c5d5c0a08ac0fbadcef2a78bc8e9abf8b37492