create new_sysimage_source_path in temp folder

[matsievskiysv]

When using Julia from Debian repository, base_dir is a write protected folder /usr/share/julia/base/. So, when creating a new app with create_app(), it fails due to lack of privileges. This PR moves temporary new_sysimage_source_path to the tmp directory, as it probably was intended.

[KristofferC]

This is not correct, the current setup requires it to be in the same folder as the rest of the Base files.

[matsievskiysv]

Well, it worked on my machine. The only place new_sysimage_source_path is used is in this call, where it's passed explicitly. After that it is deleted.

[matsievskiysv]

Just tested with sysimage.jl generated by create_app. It's not necessary to have sysimage.jl in the base folder as long as it's passed explicitly and current folder is base_dir. All these conditions are met.

[KristofferC]

Oh that is great then! Thanks!