sanitized check_as400 run script

[luxifr]

came across this and couldn't bear the state of the check script... here's a more flexible replacement...

now featuring:

• a shebang
• defaults / autodetection for classpath overridable by environment variable
• defaults for credentials file overridable by environment variable
• non-conflicting variable names
• less superfluous code
• a general call to java - make sure it's in the $PATH

Assumes the script to stay with the class files... if you want to run it from somwhere else, simply symlink it... Default location for .as400 file will be $PWD