[trac3665] Dump leases from storage to file and use this in LFC

[trac3665] Dump leases from storage to file and use this in LFC

Add the write method to lease_file_loader to dump the leaes files
from a storage container into a file.

Update the LFC code to use the lease_file_loader functions to
load the leases from the appropriate files and then to write
them to the output file and finally to move the file around.