BUG: Presence of softlink in HDF5 file breaks HDFStore.keys() (GH20523)
- [x] closes #20523 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=h1) Report
> Merging [#20537](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fac2ef1b2095c7785006c901e941e2657571d935?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20537/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20537      +/-   ##
==========================================
+ Coverage   91.84%   91.84%   +<.01%     
==========================================
  Files         152      152              
  Lines       49255    49255              
==========================================
+ Hits        45238    45240       +2     
+ Misses       4017     4015       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <ø> (ø)` | :arrow_up: |
| #single | `41.9% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/pytables.py](https://codecov.io/gh/pandas-dev/pandas/pull/20537/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3B5dGFibGVzLnB5) | `92.45% <ø> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20537/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.73% <0%> (+0.2%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=footer). Last update [fac2ef1...e0a21d6](https://codecov.io/gh/pandas-dev/pandas/pull/20537?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hi, had some newbie git issues yesterday with rebasing, but I think I resolved them now in my branch/fork - please let me know if there are outstanding issues. thanks @dworvos 