move common initialize param setting to Base
remove unused variables

warnings raised:

isolated_server/lib/isolated_server/base.rb:47: warning: assigned but unused variable - e
isolated_server/lib/isolated_server/base.rb:86: warning: assigned but unused variable - e
isolated_server/lib/isolated_server/mysql.rb:44: warning: shadowing outer local variable - pipe
isolated_server/lib/isolated_server/mysql.rb:44: warning: assigned but unused variable - pipe