set the init time in diag_integral test

[rem1776]

Description
fixes a failing unit test for diag_integral. had a uninitialized init_time value at the beginning which causes errors when writing output.

Fixes #1729

How Has This Been Tested?
amd box with gcc + openmpi

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes