[#3396] Moved column alters to new schema 22

[#3396] Moved column alters to new schema 22

configure.ac
    Added mysql/upgrade_019_to_020.sh

src/bin/admin/tests/mysql_tests.sh.in
    Updated, adjusted for version check

src/lib/mysql/mysql_constants.h
    Bumped schema version to 22

src/share/database/scripts/mysql/.gitignore
    upgrade_019_to_020.sh

src/share/database/scripts/mysql/dhcpdb_create.mysql
    Moved expire column statements into version 22 update section

src/share/database/scripts/mysql/upgrade_020_to_021.sh.in
    Removed expire column updates

src/share/database/scripts/mysql/upgrade_020_to_021.sh.in
    New file, modifies expire columns