Build script: support new options

[mitza-oci]

Change Description

Enhanced the build script with the ability to specify a prefix directory (instead of assuming HOME) and a pre-built Boost.
Cleaned up the usage message.
Moved commands that make changes on the filesystem later (after preliminary checks are done).
Removed unsupported -a "Avoid Compiling"

Consensus Changes

• Consensus Changes

API Changes

• API Changes

Documentation Additions

• Documentation Additions

[spoonincode]

Most of these changes look good but I'm concerned that the ability to set a custom prefix will mess up eosio_install.sh

[spoonincode]

tried this on a centos7 image with
scripts/eosio_build.sh -p /eosroot
but failed with
/home/spoon/eos/scripts/../scripts/eosio_build_centos.sh: line 247: /home/spoon/bin/cmake: No such file or directory

looks like some more stuff needs to be modified

[mitza-oci]

tried this on a centos7 image with
scripts/eosio_build.sh -p /eosroot
but failed with
/home/spoon/eos/scripts/../scripts/eosio_build_centos.sh: line 247: /home/spoon/bin/cmake: No such file or directory

Did it print Installing CMAKE...? Should it be using the distro's CMake?