[MC-122621] Snapshots do not function in shared hosting environments

The latest snapshots do not work properly in a shared hosting environment.

Utilizing Multicraft, each server has its own user and its own folder stored in <multicraft dir>/servers/server<id>, and that user does not have access to the overall `/servers` directory.

As it stands the snapshot attempts to create a folder outside of the server's running directory (./../backups), so that would be in <multicraft dir>/servers prompting an AccessDeniedException and preventing the server from starting.

To fix this issue, either allow setting a custom backup directory via command line, or create the backups folder in the server's running directory.

[12:20:49] [main/FATAL]: Failed to start the minecraft server
java.lang.RuntimeException: java.nio.file.AccessDeniedException: <multicraft dir>/servers/server574054/./../backups
    at bit.<init>(SourceFile:36) ~[minecraft_server.17w47b.jar:?]
    at biq.<init>(SourceFile:38) ~[minecraft_server.17w47b.jar:?]
    at net.minecraft.server.MinecraftServer.<init>(SourceFile:194) ~[minecraft_server.17w47b.jar:?]
    at pw.<init>(SourceFile:71) ~[minecraft_server.17w47b.jar:?]
    at net.minecraft.server.MinecraftServer.main(SourceFile:744) [minecraft_server.17w47b.jar:?]
Caused by: java.nio.file.AccessDeniedException: <multicraft dir>/servers/server574054/./../backups
    at sun.nio.fs.UnixException.translateToIOException(Unknown Source) ~[?:1.8.0_111]
    at sun.nio.fs.UnixException.rethrowAsIOException(Unknown Source) ~[?:1.8.0_111]
    at sun.nio.fs.UnixException.rethrowAsIOException(Unknown Source) ~[?:1.8.0_111]
    at sun.nio.fs.UnixFileSystemProvider.createDirectory(Unknown Source) ~[?:1.8.0_111]
    at java.nio.file.Files.createDirectory(Unknown Source) ~[?:1.8.0_111]
    at java.nio.file.Files.createAndCheckIsDirectory(Unknown Source) ~[?:1.8.0_111]
    at java.nio.file.Files.createDirectories(Unknown Source) ~[?:1.8.0_111]
    at bit.<init>(SourceFile:34) ~[minecraft_server.17w47b.jar:?]
    ... 4 more