There is a combinatorial explosion in this test because it tries by
default to test all pairs of available pipelines. This typically blows
up and times out in NOCODEC configurations see thesofproject#706 and others for
earlier discussions. Internally, this combinatorial explosion issue was
raised as early as November 2020! (Issues 40, 581,...)

This tiny commit does not fix the root cause but it makes a dead simple,
"quality of life" adjustment: it simply lowers the default number of
iterations from 5 to 1. There is no obvious reason why the default
should be 5 and every test plan can raise that value back up if it wants
to. Unlike thesofproject#706 which was abandoned because it reduces test coverage,
this very small change merely reduces the default test duration without
changing any of its logic.

Also, log the combination tested. Sample output:

```
declare -a pipeline_combine_lst=([0]="0 1" [1]="0 2" [2]="0 3" [3]="0 4"
[4]="0 5" [5]="0 6" [6]="0 7" [7]="0 8" [8]="0 9" [9]="0 10" [10]="1 2"
[11]="1 3" [12]="1 4" [13]="1 5" [14]="1 6" [15]="1 7" [16]="1 8"
[17]="1 9" [18]="1 10" [19]="2 3" [20]="2 4" [21]="2 5" [22]="2 6"
[23]="2 7" [24]="2 8" [25]="2 9" [26]="2 10" [27]="3 4" [28]="3 5"
[29]="3 6" [30]="3 7" [31]="3 8" [32]="3 9" [33]="3 10" [34]="4 5"
[35]="4 6" [36]="4 7" [37]="4 8" [38]="4 9" [39]="4 10" [40]="5 6"
[41]="5 7" [42]="5 8" [43]="5 9" [44]="5 10" [45]="6 7" [46]="6 8"
[47]="6 9" [48]="6 10" [49]="7 8" [50]="7 9" [51]="7 10" [52]="8 9"
[53]="8 10" [54]="9 10")
```

Signed-off-by: Marc Herbert <marc.herbert@intel.com>