'predict' should display elapsed time even for unknown ebuilds

[vincentdephily]

When a package is new, we can't predict its merge time or use the elapsed time to improve global prediction, but it would still be nice to show how long it's been merging.

Actual:

$ emlop p
Pid 7094: ... -v --backtrack=100 -av opencascade      22:25
sci-libs/vtk-7.1.0                                
Estimate for 1 ebuilds (1 unknown, 0 elapsed)             0

Desired:

$ emlop p
Pid 7094: ... -v --backtrack=100 -av opencascade      22:25
sci-libs/vtk-7.1.0                                          - 10:12
Estimate for 1 ebuilds (1 unknown, 10:12 elapsed)         0